Fix Zen Mode not closing with ESC key

### What does this MR do?

This MR fixes the ESC key not leaving Zen Mode (fullscreen).

### Why was this MR needed?

This has been broken since GitLab v7.8. The `change` event for `zen-toggle-comment` was never fired. See:

http://stackoverflow.com/questions/19505011/checkbox-checked-with-prop-does-not-fire-events-attached-to-change?answertab=votes#tab-top

### What are the relevant issue numbers?

* Closes #1025
* Closes https://github.com/gitlabhq/gitlabhq/issues/9018

See merge request !710